LONDON — A British judge upheld the arrest warrant for the WikiLeaks founder Julian Assange on Tuesday, assuring that he would remain ensconced in the Ecuadorean Embassy, where he has been for the past five and a half years.

The judge, Emma Arbuthnot, did not immediately explain her reasons, saying only, “I am not persuaded that the warrant should be withdrawn.”

After the ruling, one of Mr. Assange’s lawyers, Mark Summers, asked whether it was in the public interest to keep pursuing his client for breach of bail.

“Normally,” Judge Arbuthnot said, “such issues would only be considered if somebody were brought to court to explain their failure to surrender to bail.”

Mr. Summers replied, “There are exceptional circumstances.”

Judge Arbuthnot said she would rule on Feb. 13 on a new bid to have the arrest warrant against Mr. Assange dropped on the grounds of public interest.

WikiLeaks has published thousands of classified military documents and diplomatic cables from the American government. Once a darling of the liberal wing of the Democratic Party, Mr. Assange became persona non grata after WikiLeaks published emails that Russia had hacked from the Democratic National Committee and John Podesta, Hillary Clinton’s campaign chairman.

“No one can credibly deny that risk,” his lawyer in Britain, Jennifer Robinson, had said earlier of the prospect of a United States extradition request. “The U.S. Attorney General has said it is still a priority to prosecute Mr. Assange.”

“The head of the C.I.A. has described WikiLeaks as a hostile nonstate intelligence agency,” Ms. Robinson told an Australian online news outlet. “In these circumstances, we remain concerned about the risk of extradition to the U.S.”

Mr. Assange, 46, has been living in the Ecuadorean Embassy since 2012, after Swedish prosecutors sought his arrest over allegations of sexual assault and rape.

Sweden has since dropped the investigation, but Mr. Assange chose to remain in the embassy out of fear that of being arrested for breaching bail conditions in Britain and of being extradited to the United States.

Last month, the Foreign Office in London refused to grant Mr. Assange diplomatic immunity, which would have given him certain protections and might have allowed him to leave the embassy without facing arrest, including over a United States extradition request.